[dm-devel] DM_snapshot_cow filesystem (dmsetup create snapshot)

[Douglas McClendon]

On 11/30/2011 04:03 PM, Alasdair G Kergon wrote:
> On Wed, Nov 30, 2011 at 04:48:05PM -0500, Frederick Grose wrote:
>> snapshot Invalid  does seem to prevent even read-only access.
>
> Indeed - once it's invalid, that's the end of it.
> If we didn't do that, changes to areas of the origin that hadn't already
> changed would start to appear in the 'snapshot' and the snapshot would become a
> nonsensical hybrid of the two devices containing no information about which
> parts of it got corrupted.
>
> Don't allow your snapshots to run out of space!

So wouldn't it be much better as far as the user is concerned if, the 
instant a snapshot reached capacity, it fell over into a read-only state 
(instead of being marked invalid?), such that further corruption beyond 
such plug-pulling variety could/would not occur?  If so, would it be 
straightforward to write such a patch and would it be beneficial enough 
to end upstream?

-dmc


> If you want to see what you can recover, use that code I mentioned earlier.
>
> Alasdair
>
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